1. Field of the Invention
The present invention relates to a vehicle seat assembly comprising a seat-cushion frame supported movably in a frontward/rearward direction of a vehicle body along a pair of right and left seat slide rails mounted on a floor portion of the vehicle body.
2. Description of the Background Art
Heretofore, there has been known a vehicle seat assembly comprising an occupant seat, and a pair of right and left rectilinear slides (slide rails) which supports the occupant seat movably in a frontward/rearward direction (i.e., longitudinal direction) of a vehicle body and each of which includes a lower track member (lower rail) fixed to a floor panel in an occupant compartment and an upper track member (upper rail) slidably supported along the lower track member, wherein each of the rectilinear slides is constructed on a liner which is fixed to the lower track member and formed to have a vertical wing-shaped sidewall, and the occupant seat includes a seat cushion having a base (rear) end attached onto a rear spindle supported by a lug fixed to the upper track member, and a front end with a lower surface attached onto a spindle interlockingly connected to a front end of a lever arm which has a central portion pivotally supported by a spindle fixed to an upper portion of the upper track member of the slide, and a rear free end supporting a pin or roller adapted to be moved along an arc-shaped window formed in the vertical wing-shaped sidewall, whereby a tilting angle of the seat cushion is automatically changed as the seat cushion of the occupant seat is slidingly displaced in the longitudinal direction of the vehicle body along the rectilinear slides, as disclosed in JP 62-116324A (Hereinafter referred to “Patent Publication 1”).
Specifically, as shown in FIG. 23, in the vehicle seat moving mechanism disclosed in the Patent Publication 1, the lever arm 84 is disposed below the front end of the seat cushion 81 in such a manner that the central portion thereof is pivotally supported by a lug 83 supported by a front end of the rectilinear slide 82. The front end of the lever arm 84 is pivotally supported by a lug 85 fixed to a lower surface of a front end of the seat cushion 81, and the rear end of the lever arm 84 is slidably engaged along the arc-shaped window 88, i.e., a guide groove having a downwardly-concaved central portion, which is formed in the vertical wing (vertical wing-shaped sidewall) 87 of the lower track member (lower rail) 86. When the seat cushion 81 is moved frontwardly from a rearmost position S3 indicated by the one-dot chain line toward an intermediate position S2 indicated by the thick line, along the lower track member which is mounted on the vehicle body with a frontwardly-upward inclination, the rear end of the lever arm 84 is guided and moved downwardly by the arc-shaped window 88 engaged therewith, and thereby the lever arm has a standing posture. Thus, the front end of the seat cushion 81 is pushed upwardly by the lever arm 84, so as to allow a seating surface of the seat cushion 81 to have a frontwardly-upward inclination. Then, when the seat cushion 81 is further moved frontwardly from the intermediate position S2 toward a frontmost position S1 indicated by the thin line, the lever arm 84 is moved to have a lying posture, and thereby the front end of the seat cushion 81 is moved downwardly to reduce an inclination angle of the seating surface to a value equal to that at the rearmost position S3.
In the vehicle seat assembly as disclosed in the Patent Publication 1, tilting means comprising the arc-shaped window 88 formed in the vertical wing 87 and the lever arm 84 having the rear end slidably engaged with the arc-shaped window 88 is associated with the front end of the seat cushion 81 in such a manner as to be operable, in conjunction with the longitudinal (frontward/rearward) movement of the seat cushion 81, to vertically displace the front end of the seat cushion 81 about the rear spindle 89 disposed below a rear end of the seat cushion 81. This mechanism makes it possible to change the inclination angle of the seating surface, and vertically displace a so-called “hip point” which is a position of a hip joint of an occupant (typically driver) when the occupant sits on the seating surface, from H1 to H3 or H3 to H1, along an upwardly-convexed arc-shaped line Ma, in conformity to seated heights of occupants J1 to J3, so as to allow respective visual points I1 to I3 of the occupants J1 to J3 seated in the seat cushion 81 to come closer to an optimum line L to some extent.
On the other hand, in the above mechanism based on the lever arm 84 which is operable, in conjunction with the longitudinal movement of the seat cushion 81, to vertically displace the front end of the seat cushion 81 so as to change the inclination angle of the seating surface, it is difficulty to significantly change the hip point (H1 to H3) for the occupants J1 to J3, unless the lever arm 84 is designed to ensure a large lever ratio, for example, by extremely increasing a length of the lever arm 84, and the large lever ratio is more likely to cause a problem about instability in support of the seat cushion 81. The reason is as follows. Even if the front end of the seat cushion 81 is vertically displaced by the lever arm 84, a vertical position of the hip point (H1 to H3) located on a rear side of the front end cannot be so largely changed. Thus, the respective visual points I1 to I3 of the occupants J1 to J3 can be brought closer to the optimum line L in conformity to seated heights of the occupants J1 to J3, only if the lever ratio of the lever arm 84 is set at an extremely large value. Inevitably, the lever arm 84 having such a large lever ratio is more likely to cause wobbling at the front end of the seat cushion 81 supported thereby. Therefore, the above mechanism has a problem about difficulty in adjusting the hip point simply and adequately in conjunction with the longitudinal (frontward/rearward) movement of the seat cushion 81, in conformity to occupant's physique.
In an operation of moving the occupant seat frontwardly when an occupant having a body height fairly less than the average (hereinafter referred to as “short occupant”) sits thereon, if the inclination angle of the seat cushion 81 is reduced to bring the seat cushion 81 closer to a horizontal posture while correspondingly changing an inclination angle of a seat back to bring the seat back closer to a vertical posture, an upper body of the occupant can be moved toward a standing posture to allow an eye point of the occupant to conform to the optimum line L. However, the vehicle seat lifter mechanism disclosed in the Patent Publication 1 is designed such that the inclination angle of the seat cushion 81 is set to the same value at the frontmost position S1 and the rearmost position S3 of the occupant seat. Thus, this mechanism is incapable of obtaining a function of adjusting an eye point by changing the respective inclination angles of the seat cushion 81 and the seat back, specifically a function of displacing an upper body of the short occupant J1 to a frontwardly-inclined posture to allow the visual point I1 of the occupant J1 to conform to the frontwardly-inclined optimum line L. In this respect, there remains the need for improvement.